Avantages
NI is a very stable employer. Very little overtime and very family friendly. Some projects can be interesting, and co-workers are generally capable and friendly. If you don't want to challenge yourself or have much stress, this is an ideal place. Little is expected of you, and it takes a tremendous effort to lose your job (ideal place for slackers).
Inconvénients
There are very few chances to actually challenge yourself and get noticed. Compensation is substantially lower than other employers and tied heavily to how company is doing rather than individual performance. Many projects are tedious and not challenging. Company is very scared to invest and is trying to skate by on bare minimum and leaves many groups understaffed. They make up for the low pay with empty promises and praise. Many projects leave you gaining experience in skills that are not terribly useful outside of NI, so you become very locked into NI. Way too much Kool-Aid drinking.